Roman Numerals
The Roman Numeral symbols have the following decimal values: I=1, V=5, X=10, L=50, C=100, D=500, M=1000 The symbols are written in additive (or subtractive) order from left to right. ... That is sufficient to represent the decimal number 999999999.
M = (y2 - y1) / (x2 - x1)
m = (-2 - 2) / (4 - 0)
m = -4 / 4
m = -1
The slope of the line that goes through (0, 2) and (4, -2) is -1.